Protein Characterization is essential for the study of factors that control cell growth and differentiation. Determination of a partial amino acid sequence is often a crucial step in the characterization of a novel factor. This Core will employ both chemical sequencing and mass spectral analysis to elucidate the primary structure of proteins studied by this program. The combination of these two approaches ensures optimal sensitivity and accuracy when characterizing small quantities of novel proteins. In addition, the Core will characterize post-translational modifications such as phosphorylation which play an important role in the modulation of activity of many proteins involved in transcriptional regulation and signaling. The combination of mass spectral analysis with classical Edman degradation is especially advantageous in this field. The Core will also verify the identity of recombinant proteins used in the projects. A full characterization of the protein reagents used in experiments is essential for accurate interpretation of data. Furthermore, the Core will remain flexible to new demands placed upon it by devoting part of its resources to method development in the field of protein characterization.